Launch vehicles are generally used to launch payloads, such as satellites or scientific equipment, from the Earth's surface into space. Once in space, other on-board spacecraft propulsion systems may be utilized for orbital adjustments or transfers and attitude control. It will thus be appreciated that unlike such other on-board spacecraft propulsion systems and associated propellant tanks, launch vehicle propulsion systems and propellant tanks operate within the atmosphere and are not limited to operation in a low or zero g environment. Indeed, launch vehicles often experience a high g environment as a result of the substantial thrusts generated by the launch vehicle. As a result, launch vehicles are subject to substantial jostling due to wind and movement of thrust deflectors or the like during maneuvering.
Liquid propellant engines are used for many launch vehicle applications. Such liquid propellant engines have a number of desirable qualities including the ability to turn the engines off, as may be desired, after ignition. Accordingly, many launch vehicles include liquid propellant tanks for containing one or more liquid propellants. Among the important liquid rocket engine propellants are RP.sub.1 and LO.sub.2.
Although liquid propellant engines are advantageous for many applications, they also entail certain potential complications for launch vehicles. One of these complications relates to propellant sloshing. As noted above, launch vehicles may be subject to substantial jostling while traversing the atmosphere. As a result of this jostling, lateral forces are exerted on the liquid propellant tending to cause sloshing, i.e., non-uniform fluid flow along a longitudinal extent of the propellant tank wall and associated non-uniform distribution of the propellant across width of the tank.
Such sloshing is not a trivial concern. For example, for one proposed launch vehicle design, the portion of the total weight of the liquid propellant which sloshes will be about 24,725 pounds in the case of LO.sub.2 and 17,425 pounds for RP.sub.1. The sloshing motion of this propellant can induce significant structural loads and rigid body disturbances in the vehicle as well as potentially affecting control system operation. The potential for excitations of the sloshing resonances and their interaction with the vehicle control system are primarily driven by the location of the sloshing masses relative to the vehicle center of gravity and center of percussion, the modal frequencies and lateral modal deflections in the vicinity of the sloshing mass and the damping of the sloshing resonances. Most of these parameters cannot easily be changed should propellant sloshing dynamics become a critical issue. One exception is the propellant slosh damping.
Conventional approaches to slosh damping have generally involved installing ring baffles within the propellant tank to attenuate sloshing. Specifically, the propellant tank generally includes a cylindrical propellant containment area defined by a side wall. In some cases, the inner side wall is formed from an isogrid structure including a number of intersecting, raised ribs defining a network of cells. These isogrid structures provide a desirable combination of lightweight construction, load bearing strength and rigidity. A number of baffle rings are installed within these side walls to attenuate sloshing. Generally, these baffle rings are annular in shape and extend inwardly from the side wall, for example, six to twelve inches or more in the case of tanks having a diameter of about 12 feet. These baffles may be spaced at a longitudinal distance of, for example, two to four feet, throughout a tank slosh zone, e.g., throughout the entire propellant containment area or a portion thereof where slosh is of concern.
It will be appreciated that such baffling may involve substantial mass/weight. In one case, the dry weight of such baffles was projected to be about 350-400 pounds for a launch vehicle booster. This weight, of course, affects the total thrust requirements and/or available payload. Moreover, the fabrication and installation of these baffles increases construction complexity and overall costs.